textproduct: Rapid City

KEY MESSAGES

- Unsettled and cooler through the weekend, with daily chances for thunderstorms.

- Patchy wildfire smoke will linger through Thursday. There could be some improvement toward the end of the week.

UPDATE

Issued at 944 PM MDT Wed Aug 12 2026

03z surface analysis had a snaking frontal boundary from western MT into eastern WY and then eastern CO. Multiple outflow boundaries from earlier convection seen per radar/wind shifts. Primary batch of shra/TS east of the Black Hills seen via regional radar loop, which is ahead of a shortwave over northern WY/southeastern MT. Widening our lens, southwest flow aloft exists over the northern Plains.

Main themes of current forecast in good shape. A series of disturbances will rotate through the northern Plains tapping into sufficient moisture for daily chances for convection. In the near term, mean MUCAPE per SPC HREF <1KJ/kg Thursday afternoon with highest values over northeastern WY. 0-6km bulk shear suggests a few stronger storms may occur where solar insolation breaks out, but CAMs aren't particularly excited given paucity of stronger updraft tracks. PWATs at least 150%, so welcome rainfall will grace some folks. The most likely outcome will be a relatively rare "general" thunder risk in August over the CWA Thursday. Temperatures will be a few degrees below guidance Thursday given expected morning stratus on the western SD plains.

DISCUSSION

(This Evening Through Wednesday) Issued at 1200 PM MDT Wed Aug 12 2026

Water vapor imagery shows broad upper ridging across the south central CONUS. Upper flow over the CWA is nearly zonal, but active WSW flow over the western CONUS is quickly approaching, along with monsoonal moisture. A strong shortwave is over NW UT/eastern ID/western WY pushing eastward toward the CWA. Forcing ahead of the wave is bringing showers and thunderstorms to much of WY, including NE WY into the Black Hills and far SW SD. Deep SE low level flow is keeping moisture-rich air across the CWA even into NE WY, with dewpoints in the upper 50s to upper 60s areawide. MLCAPE of 1000- 1500 J/kg is expected as the cap quickly erodes this afternoon. 0- 6km shear will increase this afternoon to 40-60kt, supporting strong to severe storms, including isolated supercells. Large hail and damaging winds will be the main threats. Heavy rainfall will also be supported by PWATs of 150-175% of normal. CAMs show the current precip continuing northeastward, then storms developing afterward by mid afternoon across NE WY and the Black Hills area...then pushing eastward across the western SD plains. Generally quiet weather is expected overnight tonight but could still see some linger showers through early Thursday morning. Upper flow becomes more southwesterly on Thursday as another strong wave crosses the region. This will likely bring another round of high-coverage showers and thunderstorms. Instability will be slightly weaker tomorrow and shear will be much weaker, so organized severe weather is not expected. However, with PWATS nearing 200% of normal, hoping to see more much-needed precipitation though models are differing on QPF amounts and placement. Moist monsoonal flow will keep daily chances for storms across the region through the end of this and the weekend, along with near to slightly below average temps. Can't rule out strong/severe storms over the weekend.

AVIATION

(For the 12Z TAFS Through 12Z Friday Morning) Issued At 522 AM MDT Thu Aug 13 2026

Widespread MVFR-IFR conds in low clouds and fog this morning. Conds will improve later this morning, although local MVFR/IFR conds may linger around the Black Hills. Scattered showers will be possible across western SD today, with TS possible more toward evening in northeast WY. MVFR to IFR conds expected tonight across the area as moist SE upslope flow continues.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.